1. Field of the Invention
This invention relates to supports and, more particularly, to boiling water reactor control rod drive housing supports. Still more particularly, this invention relates to control rod drive housing support bars with radiation shields.
2. Description of the Prior Art
In boiling water rectors the control rod drive housing supports are generally located underneath the reactor vessel near the control rod housings. The control rod drive housing supports limit the travel of and support a control rod in the event that a control rod drive housing is ruptured. The supports prevent a nuclear excursion as a result of a housing failure, thus protecting the fuel barrier.
Typically, control rod drive housing supports consist of hanger rods that are attached and supported at their upper end at a beam structure immediately underneath the reactor pressure vessel and support bars which are bolted between the hanger rods below the control rod drives. Another grid of bars is installed on the support bars to transfer the load of a ruptured control rod drive housing to the support bars. Generally, a pair of grid bars support each control rod drive. Each pair of grid bars are held together by two grid clamps and a bolt.
In this support system of the prior art, when it is necessary to change or replace a control rod drive, the grid bars must be removed. In order to remove the grid bars the operator must manually unscrew the grid clamp bolt, remove the two grid clamps and then remove the grid bars, each weighing approximately forty pounds. The number of grid bars which must be removed depends on the number of control rods which must be replaced. Furthermore, since the grid bars are interlocking, they must be removed starting from the outer peripheral row.
Thus, if a large number of control rod drives must be replaced or if an inner control rod drive must be replaced, a large number of grid bars must be removed. The result is a time consuming and cumbersome process. Moreover, as the grid bars are heavy and awkward to handle, a dropped bar could result in serious injury. Further still, the persons handling the grid bars or working under the reactor pressure vessel are subject to substantial radiation doses. The more time a person must spend replacing the control rod drives, therefore, the more that person is subject to radiation.
Thus it is a problem in the prior art to adequately support a control rod drive housing in a boiling water reactor while allowing for quick and easy replacement of control rod drives and reducing and minimizing the radiation exposure of a person working under the reactor pressure vessel.